NASA Medallion of Space Shuttle flight

I own a medallion of the STS-3 flight march 22-30, 1982 with the wording
UNISPACE 82 on the bottom of the reverse side (Exactly like the picture on
homepage http://www.collectspace.com/). This medallion exists in two
versions WITH and WITHOUT the additional text below the three stars. See
http://www.lovaura.com/ , where the version without the UNISPACE 82 can be
found. They told me they don't know about UNISPACE 82. This was a UN
conference on space matters, see
http://www.oosa.unvienna.org/SAP/saphistory.htm
Can anybody bring some light into that darkness? If there is a reasonable
collectors value, I might consider to sell the item.
Regards Helmut WEMER